1. Field of the Invention
This invention relates to a novel method and apparatus for containing and storing low-level radioactive wastes, such as those that are generated in the nuclear power industry.
2. Description of the Related Art
Low-level radioactive wastes are typically disposed of at a different location than where they were generated. Thus, the waste must be contained through at least three distinct stages of the disposal process: processing and temporary storage of the waste at the generation site, transportation of the waste to the disposal site, and permanent containment of the waste at the final disposal site. Each of these stages presentsm different problems and requirements with respect to the containment of the waste.
During the first stage, processing and storage of the waste at the facility where it is generated, several factors are important. First, and most importantly, the container in which the waste is stored should be able to accommodate various types of waste processing equipment, discussed more fully herein. Next, it is important that the waste container be easy to handle and move about within the facility. Finally, the container should provide adequate shielding from radiation.
During the next stage of the disposal process, transportation of the waste to a disposal site, radiation shielding is of primary concern. The container must also provide protection against spillage while in transit, and, more specifically, must meet specific Department of Transportation regulations relating to the transportation of low-level hazardous wastes.
For the final stage of the disposal process, the container must be adapted to both contain the waste and provide shielding from radiation for up to several hundred years. Ease of handling, on the other hand, is of diminished importance.
Because each stage of the disposal process places different requirements on the waste container, a container that is ideally suited for use during one stage might be totally insufficient for use during another stage of the process.
Industry has typically responded to this problem by using a different containment scheme for each stage of the waste disposal process. The most widely used approach has been to hold the waste in a single primary container, such as a polymeric drum, throughout the disposal process, and combine the primary container with different components at each stage of the disposal process in order to meet the needs of that stage. Under this approach, the primary container is typically used alone during the processing and temporary storage of the waste at the generation site. The container may also be placed into or surrounded by a portable shield during this stage in order to protect workers from radiation. During the next stage of the disposal process, shipment of the waste to a disposal site, the primary container is placed inside of a protective shipping cask, typically made of lead and steel. Finally, at the disposal site, the primary container is removed from the cask and placed into another container prior to permanent storage or underground burial. This final container, often referred to as an overpack, may be made from any of a variety of materials, including concrete.
While this approach allows the individual containment requirements of each stage of the disposal process to be met, it has several disadvantages. First, the approach requires the use of a number of different types and designs of containers, casks, and overpacks. Since the components exist in a variety of shapes and sizes, care must be taken to ensure that they will be compatible with each other.
A further disadvantage of the above-described approach is that each container, cask, and overpack must be independently produced, transported, and stored before, and in some instances, after it is used. For instance, after the waste has been delivered to the disposal site, the empty casks must be removed from the site and shipped away for reuse with a compatible primary container.
A further disadvantage to this approach is that it requires excessive handling of the waste. At each stage of the waste disposal process, the primary container must be physically lifted off of the ground in order to either place it into or remove it from a cask or overpack. The risk of accidental spillage is increased each time the primary container is lifted.
Another disadvantage to this approach is that a considerable gap must be left between the outer surface of the primary container and the inner surface of the cask or overpack, in order to enable the primary container to be lifted easily into and out of the shipping cask or overpack. This results in wasted storage space, an important consideration given the fact that storage space for radioactive waste is at a premium.
Another disadvantage to this system is that since the filled primary container is at times not inside of a cask or overpack, and since even when it is inside of a cask or overpack, the cask or overpack provides no direct structural support to the container to assist it in withstanding the outward forces that are imparted on it by the contained waste, the primary container must strong enough, by itself, to withstand all such forces. Thus, when it is combined with a shipping cask or overpack, there is a great deal of structural redundancy in the system.